The invention relates generally to contaminant control systems and more particularly to a method and system which enables workers to work in an enclosed radioactive workspace safely for longer periods with greater freedom of movement in the workspace.
In nuclear power plants, steam generators typically are utilized as heat exchangers between the reactor and a power generating steam turbine. The steam generators have hundreds or thousands of heat exchange tubes in single pass or double pass loop tubes inside the generator housing. The tubes carry contaminated water, at high temperature and pressure from the reactor, through the generators, which in turn transfers heat to water around the tubes, creating steam to drive the turbine. Periodically, typically during a reactor refueling outage, or if a leak occurs, the tubes are checked to make sure they are not leaking or stressing to the point where they will leak contaminated water into the steam.
The tubes are checked by running a tester, typically an eddy current tester, over the length of each tube to be checked. Typically, unless a leak has occurred, some predetermined number of the thousands of tubes are checked during each outage so that during a period of time all the tubes are checked. The testers are operated and repairs or sealing off of leaking tubes are sometimes performed by workers physically climbing into the steam generators through a manway or portal in the generator housing. The interior of the generators, which typically are sixty feet high, present workers with the problems of a high radiation environment and contact contamination with radioactive airborne particles which are on the interior surfaces of the housing and are dislodged by the workers themselves from the tubes and surfaces.
Due to the fact that the interior or workspace of the generator is a high radiation environment, the workers are only permitted to be inside the generator for a few minutes at a time. The checking and repairs, therefore may require hundreds of entrances and exits. Many attempts to shield the radiation of the interior walls and tubes of the generator have been attempted with limited success. These decontamination approaches are very expensive and create radioactive wastes.
Further, the problem of contact contamination within the workspace requires respiratory protection for the workers, as well as causing surface contamination of the workers garments, which contamination is then brought out of the generator when the workers climb out of the portal. Each worker typically is attired in several layers of clothing covered by a plastic outer layer and a self contained breathing apparatus or supplied-air respirator. This makes it difficult to pass through the portals, which usually are small on the order of sixteen inches in diameter, and the clothing itself is cumbersome to work in.
Further, each time the worker leaves the generator at least the outer clothing which has radioactive contaminants on it has to be removed and disposed of. The area around the portal becomes contaminated and must be cleaned. The workers outside the generator are exposed to the contaminants brought out on the clothing and the worker himself is further exposed because the contaminants are in physical contact with the clothing and remain there while the clothing is further handled and disposed of.
The invention permits workers to work in a cool, comfortable radiation attenuated environment without cumbersome extra clothing. The workers pass into and out of the enclosed workspace of the steam generator through the system of the invention without physical exposure to the contaminants and without carrying contaminants outside the workspace. The radiation emitted by the surfaces and tubes of the generator, particularly the lower end portion of the tubes, is absorbed by a radiation attenuating fluid of the system. Thus, the length of exposure to the workers is reduced, the amount of material to be disposed of is greatly reduced and contamination of workers and outside areas are sustantially eliminated. Further, the contaminants are not handled because the contaminants are filtered by the present invention and removed from the enclosed workspace.